Control apparatus



y 4, 1965 R. c. FLOM 3,181,441

CONTROL APPARATUS Filed Oct. 12, 1961 2 Sheets-Sheet 1 INVENTOR. RIQ ARDL. 1.

ATTORNEY May 4, 1965 c, FLOM CONTROL APPARATUS 2 Sheets-Sheet 2 FiledOct. 12. 1961 LAN-1|- A ,m :m

INVENTOR. RICHARD C JZQ Z BY flTTORA/E) United States Patent 3,181,441CONTROL APPARATUS Richard C. Flom, Minneapolis, Minn., assignor t0Honeywell Inc., a corporation of Delaware Filed Oct. 12, 1961, Ser. No.144,667 14 Claims. (Cl. 94-46) The present invention is concerned withan improved control apparatus particularly adapted for use with roadpaving machines of the floated screed type.

Many roads are surfaced with a bituminous material to form what iscommonly called a blacktop road. Such roads may be produced by machinesincluding a hopper into which the bituminous material is deposited andout of which the bituminous material is fed, immediately in front of thescreed, to be deposited on the surface to be paved, the screedcompacting the bituminous material to form the paved road surface. Thus,the screed is effective to control the height or grade of the resultingpaved road as well as the slope of the road, it being recognized thatsuch a road is normally crowned at the center and sloped toward theouter edges, and is also sloped at curves which are formed in the road.

A type of paving machine of this general construction utilizes afloating screed which freely rests upon the paved surface by virtue ofthe weight of the screed and in which the angle of attack, that is theattitude of the bottom surface of the screed, determines the height ofthe resulting paved surface. More specifically, such a paving machine isprovided with a propulsion unit which includes a pair of crawler treadsor wheels disposed at each side of the propulsion unit, to move theunit. The forward end of the propulsion unit is provided with a hopperto receive the bituminous material. This bituminous material is fed outof the rear portion of the propulsion unit onto the surface to be paved.This operation is provided as the propulsion unit moves along theroadway to be paved. Positioned behind the propulsion unit is a floatingscreed which is attached to the propulsion unit and towed thereby bymeans of a pair of beams, the forward ends of which are freely pivotedto the propulsion unit at each side of the unit. The rear ends of thebeams are rigidly attached to the screed. Thus, as the paving machinemoves, the bituminous material is supplied from the hopper to theroadway to be paved immediately in front of the screed, and the screedcompacts this materialas the paver moves. The height of the resultingroad surface is normally controlled by controlling the attitude of thescreed by means of screed adjusting screws located at the rear end ofthe beams. However, should the forward ends of the beams be moved in anupward direction, the angle of attack of the screed is changed (theforward edge is tilted up) and a thicker road is produced to increasethe height of the road as the screed climbs on top of the bituminousmaterial deposited in front of the screed. Should the forward end of thebeams be lowered, the angle of attack of the screed is again changed(the forward edge is tilted down) and the screed tends to dig into thebituminous material, as the paving machine moves, to thus form a thinnerlayer of bituminous material and to lower the height of the resultingroad surface. Furthermore, if the forward end of one of the beams israised as the forward end of the other beam either remains stationary oris lowered, then the transverse slope of the screed is changed and theresulting slope of the paved road surface is likewise changed.

The present invention is concerned with an improved automatic controlapparatus for automatically controlling the attitude of the screed tothus provide a road surface having a height established by apredetermined height datum means which has been disposed along the icesurface to be paved, and likewise having a slope which is manuallyselected and automatically controlled.

My invention provides a pair of sensors including transducers in theform of potentiometers whose wipers are controlled by sensors, one ofthe wipers being controlled by a height sensor disposed on one of thebeams, and the other wiper being controlled by a pendulum sen.- sor.These potentiometers constitute portions of two A.C. bridge circuits,each bridge circuit including a further manually controllablepotentiometer. The first bridge circuit associated with the heightsensor (called the Follower Sensor) is provided with a vernieradjustment potentiometer such that the output of this bridge circuit maybe nulled as the paving machine is initially brought into engagementwith the height sensor contacting or cooperating with the height datummeans. Thus, the paving machine is initially adjusted to produce thedesired height and thickness of paved surfaces. The second A.C. bridgecircuit is associated with the floated pendulum and is provided with aslope adjustment potentiometer which is calibrated so as to allow theoperator of the paving machine to manually adjust the slope of thescreed and to change this slope as certain conditions are met, such asthe forming of a curve in the road.

A further feature of my invention is the provision of a pair ofindicating meter circuits which are connected one to each of the twoA.C. bridge circuits to thus provide an indication of the operaiton ofthe control apparatus, indicating respectively the grade or height errorand the slope error.

The output of each of the bridge circuits is also fed to first andsecond motor control circuits, respectively. These motor controlcircuits are phase-sensitive circuits having silicon controlledrectifier output circuits to provide reversible polarity D.C. voltageoutput.

In the preferred embodiment of my invention the position of each of thebeams is controlled by a reversible .C. motor which is operativelyconnected thereto. It is within the teachings of my invention toselectively control either of these beams by the pendulum or by theheight sensor. This is accomplished by a manual switch which selectivelyconnects the output of the first or second motor control circuits to oneor the other of the D.C. motors which are associated with the beams.Thus, my apparatus provides a means whereby the pendulum may be switchedto control one or the other of the beams, the height sensor also beingswitched to control the beam which is at that time not being controlledby the pendulum, A more desirable arrangement of the switching providestransfer of low power signals in the electronics instead of switchingmotor loads.

A further feature of my invention is the provision of further pair ofmanual switches having a manual and an automatic position, one of theseswitches being connected with the pendulum and the other of the switchesbeing connected with the height sensor. Thus, the operator of the pavingmachine may selectively control the paving machine automatically or maycontrol the machine manually utilizing a switch which may be pulsed ormomentarily closed to control the positions of the beams manually. Theabove mentioned indicating meter circuits are at all times connected toone of the sensing means (the pendulum or the height sensor) and thusthe indicating meters indicate to the operator the nature of the manualcontrol which he is maintaining.

While the present description deals with an electrical system havingelectric motors, it is within the teachings of my invention to providemeans to control hydraulic motive means, such as hydraulic rams.

The preferred embodiment of my invention will be ap-v parent to thoseskilled in the art upon reference to the following specification,claims, and drawings, of which:

FIGURE 1 is a view of a paving machine of the floating screed type,showing portions constituting elements of my invention,

FIGURE 2 is a simplified showing of portions of the paving machine ofFIGURE 1, showing the screed in diagrammatic form, the beams which areattached, one to each side of the screed, and showing the pendulumsensor and following sensor, as well as the reversible DC. motors whichare operative to control the vertical position of the pivots of thebeams, and

FIGURE 3 is a schematic representation of my electronic control systemwhereby the slope and grade of the resulting road surface is selectivelyautomatically controlled or manually controlled, in accordance with themode of operation of my invention which is selected by the operator ofthe paving machine.

Referring specifically to FIGURE 1, reference numeral identifiesgenerally a paving machine having a propulsion unit 11 including ahopper 12 and crawler type treads '13. This propulsion unit 10 includesa motor connected to drive the treads 13, one of which is disposed ateach side of the paving machine 10. The hopper 12 of the paving machineis adapted to receive bituminous material, usually dumped into thehopper by a truck which hauls the bituminous material between theroadbed to be paved and the plant which is producing the bituminousmaterial. The paving machine 10 is adapted to be operated by an operatorpositioned on the paving machine, and reference numeral 14 identifies acontrol box whereby the operator may selectively automatically ormanually control the road surface which is being produced by pavingmachine 10. The method of achieving automatic or manual control will beevident from the following description.

Reference numeral 15 identifies a roadbed which is to be paved and alongwhich a height reference datum 16 is provided, this height referencedatum consisting of a wire, string, or the like which has beenpreviously placed in position alongside the roadbed 15 at apredetermined height. Reference numeral 17 designates a finished roadsurface which has been produced by the paving machine as it moves in aforward direction, that is to the right as shown in FIGURE 1.

The height datum may also be obtained from a previously produced roadbedmat, for purposes of matching one mat to another.

Reference numeral 20 identifies generally a screed construction which isrigidly attached to a beam 21, pivoted to the propulsion unit at aforward pivot 22. The paving machine 10 of FIGURE 1 is provided with apair of beams, one of which is positioned at each side of the propulsionunit. Each of the beams is pivoted at its forward end. The attitude ofthe screed, that is the angle of attack of the lower surface 23 thereof,may be initially manually controlled by means of a pair of screededadjusting screws 24 and 25 which can be turned by the operator of thepaving machine to control the angle of attack of the screed. Bituminousmaterial is fed from hopper 12 to a spreader type mechanism 26 which iseffective to spread the bituminous material on the roadbed 15immediately in front of screed 20, where the material is compacted bythe screed into the finished road 17. The screed assembly 20 may includea vibrating mechanism or tamping mechanism as well as a means forheating the bituminous material deposited under and in front of thescreed.

My invention is concerned with an improved control apparatus forautomatically controlling the screed 29 in a manner to produce apredetermined desired finished road 17. This is accomplished by meansincluding a follower sensor 27 cooperating with the height datum 16, andby means of a pendulum sensor 30.

Referring now to FIGURE 2, in this figure I have shown a simplified viewof the screed, its supporting beams, their pivot points, and thefollower sensor and pendulum sensor. As in FIGURE 1, the screed assemblyis identified by the reference numeral 20 having a bottom surface 23.Beam 21 having pivot 22 is shown as is the other beam disposed at theback side of the paving machine as shown in FIGURE 1. This beam isidentified by reference numeral 31 and is provided with a pivot 32.Follower sensor 27 is shown adjustably positioned on beam 21 and inengagement with the height datum 16. Pendulum 30 is supported on atransverse beam 33 which is pivotally mounted at a pair of uprightsupports 34 and 35 associated with the beams 21 and 31 respectively.Thus, as the pivot points of beams 21 and 31 move up and down, the beam33 is maintained in transverse alignment with the pivot points 22 and32. Pendulum 30, responsive to gravity, thus assumes a positionindicative of the slope of the transverse beam 33. The height of thepivots 22 and 32 is controlled by a pair of pivot adjusting screws 36and 37 whose positions are controlled by a pair of reversible D.C.motors 40 and 41.

As mentioned, screed assembly 20 floats on the bituminous materialdeposited thereunder and is attached to the propulsion unit 11 by meansof the pivots 22 and 32. Thus, the angle of attack of the bottom surface23 of this screed is controlled by the vertical movement of these pivotpoints. Should the pivot points 22 and 32 be driven in an upwarddirection, the bottom surface 23 of the screed assembly is tilted in anupward direction and thus the screed climbs up on top of a greaterthickness of hituminous material which is deposited under the screed.Thus, the height of the finished road surface 17 is increased. Shouldthe pivot points 22 and 32 be lowered, the bottom surface 23 of thescreed assembly is tilted in a downward direction and the screed tendsto dig into the bituminous material deposited in front of the screed andthus the finished road surface 17 is reduced in thickness, that is theheight is decreased. Furthermore, the transverse slope of the finishedroad surface 17 may be controlled by raising or lowering the pivots 22and 32 in a differential fashion. Thus, if pivot 22 is lowered whilepivot 32 is raised, screed assembly 20 is tilted to raise the right handend as seen in FIGURE 2 while lowering the left hand end. Thus, theresulting road surface 17 is sloped toward the height datum 16.

During the paving operation there are several input disturbances thatcan upset the screed setting and the ability of the machine to lay thedesired smooth mat. These disturbances are: (l) roughness of thesubbase, or surface being pave-d, which causes vertical motion of themachine 10 and hence the pivot points 22 and 32; (2) variations incompaction of the bituminous material which results in a change invertical displacement of the screed 20 for a given ski angle setting ofthe screed bottom 23 as the machine 11 travels forward; and (3) a changeof the setting of the screed adjusting screws 24 and 25 which results ina change of the attitude of the screed bottom 23 relative to the pivotpoint heights 22 and 32.

Mounting of the follower sensor 27 between the pivot point 22 and thescreed 20 will cause the control system to compensate for all of theseabove mentioned disturbances. Placement of the sensor 27 closer to thepivot point 22 will result in favoring item (1) above. Moving the sensor27 horizontally toward the screed 21) will result in favoring correctionfor items (2) and (3) above. In essence correction to a step disturbancewill occur in a shorter distance of travel for the aforementionedconditions.

The same arguments are true for the transverse or slope control andapply to the attachment points 34 and 35 of the transverse beam 33 tothe screed tow beams 21 and 31.

Since the control system maintains the transverse beam 33 at apreselected angle with respect to gravity by means of pendulum 3f), thefinal mat surface 17 will be parallel to the transverse beam 33 only ifthe screed adjusting screws 24 and 25 are at the same setting such thatboth sides of the screed bottom 23 are at the same angle with respect tothe tow beams 21 and 31. This is not a necessary condition to laying thedesired mat surface 17, but unless the condition is met externalcalibration means are required.

Referring now to FIGURE 3, in this figure I disclose a schematic diagramof an electronic circuit by which the paving machine and thus thefinished road surface may be manually or automatically controlled at theoption of the operator of the paving machine. In this figure I disclosetwo channels, one of which is operative with the pendulum sensor and theother of which is operative with the follower sensor. The outputs ofeach of these channels may be selectively connected to control the DC.reversible motors 40 and 41 under the control of manually operableswitch means 42.

The basic components of my control system constitute A.C. bridgecircuits 43 and 44, meter drive circuits 45 and 46 connected toindicating meters 47 and 48 respectively, and motor drive circuits 5iand 51 which provide a reversible polarity DC voltage across outputresistors 52 and 53 respectively. As will be apparent, the outputresistors 52 and 53 may be selectively connected to either of the motors40 and 41, depending upon the position of the manual switch 42.

To avoid the switching of high magnitude motor currents, resistors 52and 53 may be directly connected to motors 41 and 46 respectively andswitch 42 may be connected to switch the control signals at the primarywindings of transformers 104 and 112, For example, in one position ofswitch 42, when so connected, unijunction transistor 111 is connected tosilicon controlled rectifier 113 and unijunction transistor 193 isconnected to silicon controlled rectifier 105. The other position ofswitch 42 reverses this interconnection of the unijunction transistors Iand silicon controlled rectifiers. As disclosed in FIGURE 3, the outputof the channel connected to the wire follower, that is resistor 53, isconnected to control motor 40 and thus control pivot point 22 of beam21. The output of the motor drive circuit connected to be controlled bythe pendulum sensor, that is resistor 53, is connected to control motor41 and thus to control pivot point 32 of beam 31.

It is within the teachings of this invention to not only provide switch42 to reverse the control of motors 40 and 41 but by this means providemeans whereby the wire follower sensor 27 may be mounted on the otherside of the paving machine from that shown in FIGURE 1, namely on beam31 rather than on beam 21 as shown in FIGURE 2. The follower sensor mustcontrol the motor on the side the sensor is mounted by proper selectionof switch 42s position.

Considering the schematic diagram of FIGURE 3 in greater detail, thelower portion of the figure will first be considered, that being theportion controlled by the follower sensor. The follower 27 of FIGURES land 2 is mechanically connected by means identified by reference numeral54 to control the position of wiper 55 of potentiometer 56 having aresistance element 57. Potentiometer 56 constitutes a portion of theA.C. bridge circuit 44 whose input voltage is supplied by means of atransformer 60 having a primary connected to a source of alternatingvoltage, not shown. This A.C. bridge circuit 44 includes a furtherpotentiometer 61 designated a Vernier adjustment potentiometer having aresistance element 62 and a manually adjustable Wiper 63. A.C. bridgecircuit 44 also includes a pair of resistors 64 and 65 which areconnected in series, the series connected resistors being connected inparallel with the resistance elements 57 and 62 of potentiometers 56 and61 to the supply voltage for the bridge. Reference numeral 66 identifiesa manual switch having a normal open position and having a pair ofclosed positions to which the switch may be moved and held, the switchreturning to its center position upon being released.

The input of meter drive circuit 46 is connected to bridge 44 at aterminal 67 and at a manually adjustable potentiometer wiper 7d. Theresistance element "1'1 cooperating with potentiometer wiper 70 has oneterminal connected to the wiper 63 of the Vernier adjustmentpotentiometer and the other terminal connected to the wiper 55 which iscontrolled by the wire follower sensor 27.

The input of the motor drive circuit 51 consists of a grounded terminal72 and a further terminal 73 which is connected to the movable blade ofmanual switch means identified generally by means of reference numeral74. This manual switch means 74 constitutes the automatic and manualswitch of my apparatus whereby the operator of the paving machine 10 mayselect automatic or manual control of the pivot points 22 and 32 ofbeams 21 and 31. Switch means 74 includes a pair of movable switchblades 75 and 76 which cooperate with stationary contacts 77 and 7 8 inthe automatic position of the switch means and which cooperate withstationary contacts 89 and 81 in the manual position of the switchmeans. With switch means 74 positioned in the automatic position, asshown in FIGURE 3, input terminal 72 of the motor drive circuit 51 isconnected through switch blade 75 and contact 77 to potentiometer wiper55, the position of which is controlled by the wire follower sensor 27.The other input terminal 73 of the motor drive circuit 51 is connectedby switch blade 76 and contact 78 to the wiper 63 of the Vernieradjustment potentiometer 61.

Should the switch means 74 be positioned in the manual position, thenthe input terminal 72 of motor drive circuit 51 is connected by switchblade 75 and contact 8% to a terminal 82 connected between resistors 64and 65. Thus, the input terminal 72 of the motor drive circuit 51 iseffectively connected to a fixed A.C. potential level. The inputterminal '73 of motor drive circuit 51 is connected by means of switchblade 76 and contact 81 to the manual switch means 66. Thus, when themanual switch 66 is moved in an upward direction, a contact 83 and aresistor 84 connect terminal 73 to an A.C. potential of a first level,whereas when switch 66 is moved in a downward direction to engagecontact 85, input terminal 73 is connected through a resistor 86 to asecond A.C. potential level. Thus, with switch 74 in the manual positionswitch 66 may be pulsed to engage either contacts 83 or to achieve thedesired direction control of the motor connected to the output 53 ofmotor drive circuit 51.

Thus far, the explanation of my invention has concerned itself primarilywith the description of the operation of A.C. bridge circuit 44. Thisdescription of operation can be readily applied to bridge circuit 43wherein a potentiometer wiper 87 has its position controlled by thependulum sensor 30. A slope adjustment potentiometer 90 having amanually adjustable wiper 91 is connected to form a portion of A.C.bridge circuit 43 in much the same manner as the Vernier adjustmentpotentiometer 61 of bridge circuit 44, above described. Resistors 92 and93 are provided, corresponding to resistors 64 and 65 of bridge circuit44. Reference numeral 94 identifies a manual switch having an automaticand a manual position to control the input to motor drive circuit 56) atterminals 97 and 98, in much the same manner as described in connectionwith motor drive circuit 51.

In normal operation of the paving machine 16 of FIG- URE 1 the operatorfirst activates the automatic control system with the switch means 74and 94 in the manual position. By means of manual switch 66 the pivotscrew 36 is controlled to position pivot point 20 at its approximatemidpoint position. The slope adjustment potentiometer 9t) is set at thedesired slope setting and switch 94 set to the Auto position. This willresult in the screw 37 driving the pivot point 32 to a vertical positionthat will maintain the angle of the transverse beam 33 at the desiredslope angle. The propulsion unit 11 is then activated to start thepaving operation, and the screed screw 24 is controlled to produce thedesired mat thickness of 7 bituminous material on the right side ofscreed 20. The screed screw 25 must be adjusted the same as screed screw24- to keep the two sides of the screed synchronized.

This initial manual control is necessary because of the fact that thebituminous material compacts under the screed assembly 20 and thiscompaction varies with the mix being received from the hopper 12. Whenthis desired bituminous mat thickness has been achieved, the propulsionunit 11 is stopped and the height of the follower 27 is adjusted on beam21 such that the grade error meter 48 is near its null position as shownin FIGURE 3. The grade error meter 40 is then brought to the absolutenull position by manual movement of the Vernier adjustment potentiometerwiper 63. Switches 94 and 74 are now set to their automatic position andthe propulsion unit 11 moves in a forward direction to produce thefinished road surface 17 at the height selected by the height datum 16and at the slope controlled by the slope adjustment potentiometer wiper91.

In unusual situations of large slope requirements or large deviations ofthe existing surface (to be repaved) from the desired slope, theprocedure outlined above may not be satisfactory due to limitations inthe mechanical travel of pivot point screws 36 and 37. Such a case mayrequire initial differential setting of screed adjusting screws 24 and 2so as to keep the pivot points 22 and 32 reasonably close to the centerof travel of pivot screws 36 and 37 when the desired mat thickness andmat slope are achieved during initial manual operation. When this isdone, the slope potentiometer 90 calibration will not correspond to matslope. There will exist a constant offset angle that can be readilymeasured and the slope potentiometer 90 offset by the required amount.Switches 74 and 94 can now be set to their automatic position and thepaving operation started.

Once the calibration has been obtained, the screed adjusting screws 24and 25 should not be changed. Small variations in mat thickness can beobtained by changing the setting of the Vernier adjustment potentiometer61 and slope variations obtained by changing the setting of the slopeadjustment potentiometer 90.

As the paving progresses, the operator may change the slope of theresulting roadbed, for example as the paving machine rounds a curve tobe formed in the road. Furthermore, the degree of automatic controlbeing achieved by my invention may at all times be observed by referenceto the slope error meter 47 and the grade error meter 48, these metersbeing contained within the control box 14 as shown in FIGURE 1.

Referring now specifically to the motor drive circuit 51, the triggeramplifier of the motor drive circuit receives its energizing voltagefrom a full wave rectifier, unfiltered, and clipped source 101. As aresult of this circuit, the supply voltage present at terminal 200 (andterminal 201 for motor drive circuit 50) consists of a series oftrapezoid shaped pulses, having a steep leading edge, a flat topportion, and a steep trailing edge joining the leading edge of the nextpulse. Capacitor 202 charges through resistor 203when terminal 200 ispositive. Conduction of transistor 102 modifies the charging rate bymeans of forming a shunt path around capacitor 202. In the absence of aninput signal potentiometer 204 is adjusted to provide conduction oftransistor 102 such that the voltage across capacitor 202 is notsufficient to cause firing of unijunction transistor 103 during the flattop portion of the voltage wave form at terminal 200. As the voltagefalls on the trailing edge of the wave form at 200, the unijunctiontransistor 103 will fire. Thus the capacitor 202 is discharged at theend of each half cycle and therefore is synchronized to line frequency.

As an A.C. control signal is derived from bridge 44, transistor 102 isrendered less conductive for a particular half cycle, depending upon thephase of this control signal. With transistor 102 less conductive,capacitor 202 now charges more rapidly (its shunt path has been at leastpartially removed) to the firing voltage of unijunction transistor 103.The rate of charging of capacitor 200 depends upon the state ofconduction of transistor 102, this in turn being controlled by themagnitude of the control signal, the greater the magnitude of thecontrol signal, the less the conduction of transistor 102. As a result,the unijunction transistor 103 is rendered conductive during the flatportion of its supply voltage pulse. When unijunction transistor 103fires, capacitor 202 is discharged through the primary of transformer104, generating a secondary pulse from transformer 104 which firessilicon controlled rectifier 105, resulting in a D.C. voltage developedacross resistor 53. Larger magnitude control signals produce earlierfiring of the silicon controlled rectifier 105 during the particularhalf cycle, resulting in a greater average D.C. across resistor 53.Reversal of the phase of bridge 44 control signal causes firing of thesilicon controlled rectifier 105 during the opposite half cycleresulting in a reversal of the D.C. voltage across resistor 53. Thus,depending upon the phase and magnitude of the input voltage applied fromthe A.C. bridge circuit 44 to transistor 102, unijunction transistor 103is effective to control the conduction of silicon controlled rectifier105 and produce a D.C. voltage of a polarity which is reversible withthe phase of the A.C. signal voltage applied from bridge circuit 44 andof a magnitude corresponding to the magnitude of bridge voltage. Thus,reversible control of motor 40 is achieved.

By way of a specific example, if it is assumed that the propulsion until11 drops into a hole which exists in roadbed 15, then the pivot points22 and 32 of beams 21 and 31 will drop in a downward direction and wirefollower 27 will also be lowered. As wire follower 27 lowers, theposition of potentiometer wiper 55 is altered and an input signal isapplied to not only the input of meter drive circuit 46 but also to theinput of motor drive circuit 51. The phase of the A.C. voltage appliedto the input of motor drive circuit 51 is such as to control theconduction of silicon controlled rectifier 105 to produce a D.C. voltageacross resistor 53 of a polarity which causes rotation of motor 40 todrive the pivot point 22 of beam 21 in an upward direction to thusrestore the relative position of sensor 27 and height datum 16. Further,since pendulum 30 is responsive to the relative positions of the beams21 and 31, the raising of pivot point 22 causes the transverse attitudeof beam 33 to also change. This change in attitude of beam 30 is sensedby pendulum 30 to affect a corresponding control of its motor 41 to thuschange the attitude of the bottom surface 23 of the screed, causing athicker mat of bituminous material to be laid at this portion of theroadbed, thus compensating for the hole which is present in the roadbedand manitaining the finished road surface 17 at the reference datum 16and at the slope which has been selected by means of the slopeadjustment potentiometer wiper 91.

The above description has concerned itself with the motor drive circuit51. Motor drive circuit 50, cooperat ing with A.C. bridge circuit 43corresponds to motor drive circuit 51 and is provided with a transistorcontrolling a unijunction transistor 111, the output of unijunctiontransistor 111 being provided at a transformer 112 whose secondary isconnected to control the conduction of a silicon controlled rectifier113 constituting a portion of a bridge rectifier 114 whose supplyvoltage is derived from a transformer 115 connected to the source ofalternating voltage. Thus, as above described in connection with thewire follower 27, should the paving machine 10 tilt in a transversedirection, again due to irregularities in the roadbed 15, this tiltingof the paving machine is sensed by pendulum 30 to adjust the position ofwiper 87. An A.C. input signal of a given phase is then applied to theinput of motor drive circuit 50 to control transistor 110 and in turn tocontrol unijunction transistor 111. Unijunction transitsor 111 iseffective to control the conduction of silicon controlled rectifier 113to provide a D.C.

voltage at resistor 52 having a polarity to affect operation of motor 41to restore pendulum 3t), and thus screed assembly 29 to its desiredslope. For example, if it is assumed that the propulsion unit 11 of thepaving machine tilts so as to lower the pivot point 32, pendulum 30 iseffective to sense this resulting change in attitude of beam 33 andpotentiometer wiper 8'7 associated with the pendulum is moved to providean A.C. input signal to motor drive circuit 50 to produce control ofsilicon controlled rectifier 113 resulting in a DC voltage presentacross resistor 52 which is of a polarity to drive motor 41 to effect anupward movement of pivot point 32 of beam 31 to restore the desiredattitude of beam 33 and thus the desired slope attitude of screedassembly 20.

Referring noW specifically to the meter drive circuit 46 associated withthe A.C. bridge circuit 44, this meter drive circuit transsistor 124derives its energizing voltage from a pair of diodes 120 and 121connected to the secondary Winding of a transformer 122 whose primary isconnected to the source of alternating voltage. The DC. voltageresulting from diodes 121) and 121 is supplied across a resistor 123,which voltage is effective to supply operating voltage to a firsttransistor 124. This first transistor is connected in controllingrelation to a second transistor 125, the second transistor receiving itssupply voltage from the secondary of transformer 122 by way of a furtherpair of diodes 126 and 127, these diodes being connected to thecollector electrode of transistor 125 through resistors 128 and 129. Theoutput of meter drive circuit 46 consists of a capacitor 130 which isconnected to the grade error meter 48, this meter being a DC. meter ofthe center position null type. The A.C. signal present at inputterminals 67 and 70 of meter drive circuit 46 is amplified by transistor124 and is applied to the input electrode of transistor 125 to causethis transistor to conduct such that one half cycle of conduction isgreater than the other half cycle of conduction, depending upon thepolarity of the A.C. voltage present at input terminals 67 and 70. Thevoltages developed across resistors 128 and 129 (during the alternatehalf cycle above mentioned) will be of unequal magnitude, one voltagebeing larger than the other, corresponding to that half cycle duringwhich transistor 125 conducts to a greater degree than it does on theother half cycle. Thus, capacitor 130 is charged as a result of thevoltage differential across resistors 128 and 129 and a voltage of onepolarity or another is applied to meter 48, depending upon the phase ofthe A.C. input voltage applied at terminals 67 and 70. It of coursefollows that with the relative position of the wire follower 27 andheight datum 16 as desired, the output of bridge circuit 44 is at a nullposition and likewise meter 48 is nulled to indicate that the roadbed 17is being produced at the desired height. Potentiometer 131 provides anA.C. signal to the electrode of transistor 124 to null the meter underthe conditions of zero signal at terminals 67 and 70.

The meter drive circuit 45 associated with A.C. bridge circuit 43corresponds to meter drive circuit 46 above described. Here again, atransistor 141i is connected to control .a transistor 141. Transistor141 in conjunction with resistors 142 and 143 and diodes 144 and 145, iseffective to control the charge on a capacitor 146 which is connected tothe slope error meter 47, this meter being of the null reading D.C.type. In this case, so long as the roadb ed 17 is being formed at theslope which has been selected by adjustment of the slope adjustmentpotentiometer wiper 91, the A.C. output of bridge 43 is at a null andthe slope error meter 47 is likewise at a null position.

A further feature of my invention resides in the fact that my meterdrive circuits 45 and 4d are at all times connected to the output of therespective bridges 43 and 44 and thus the slope error meter 47 and thegrade error meter 48 are effective to indicate to the operator of thepaving machine the degree of correlation between the resuiting roadsurface 17 and that which has been selected by the slope adjustmentpotentiometer wiper 91 and the height datum 16. This is true even thoughthe switch means 74 or 94 are switched to the manual position whereincontrol of either or both of the pivot points 22 and 32 of the beams 21and 31 may be manually controlled .by the manual switches 66 and 1%.Thus, the paver may be manually controlled by means of switches 66 andand the meters 47 and 48 may be observed by the operator todetermine thedegree of control which he is efiecting by manual means.

While the description has dealt with the position of manual switch 42wherein motor 41 is connected to be controlled by motor drive circuit 51and thus by means of wire follower 27, it is within the teachings ofthis invention to reverse the control of the motors 4t) and 41 such thatmotor 41 is now controlled by follower sensor 27 and motor 41) iscontrolled by pendulum 30, when the sensor 27 is moved to beam 31.

It is recognized that further embodiments of my invention will beapparent to those skilled in the art and it is thus intended that thescope of the present invention be limited solely by the scope of theappended claims.

I claim as my invention:

1. Control apparatus for use with a paving machine of the floated screedtype wherein the screed rests upon the paved surface being formed and istowed by a propulsion unit to which it is pivotally attached by means ofa pair of forwardly extending beams, the rear ends of the beams beingrigidly fixed to the screed, the control apparatus functioning toautomatically control the angle of attack of the two ends of the screedin relation to the paved surface to thereby vary the height and slope ofthe surface as the machine moves to deposit paving material under thescreed, with the height being established by a height datum disposedalong the route to be paved, the apparatus comprising; a pair ofelectric motors, one of which is associated with each of the beams toindependently move the same uipon energization of its motor and therebyindependently change the angle of attack of the two ends of the screed;height sensing means mounted on one of the beams to move therewith andto cooperate with the height datum, said height sensing means includinga :potentiometer having a resistance element and a wiper whose positionis controlled by the relative spacing of said height sensing means andthe height datum; a Vernier adjustment potentiometer having a resistanceelement and a manually movable wiper; a first source of voltage, meansconnecting the resistance elements of said height sensing meanspotentiometer and said Vernier adjustment potentiometer in parallel tosaid first source of voltage, first motor control means having an outputand having an input which is connected to the Wipers of said heightsensing means potentiometer and said Vernier potentiometer; slopesensing means mounted on the beams and having a potentiometer with aresistance element and a wiper controlled by a pendulum, the position ofsaid wiper being indicative of the slope of the screed and the angle ofattack of the two ends of the screed; a slope adjustment potentiometerhaving a resistance element and a manually movable wiper; a secondsource of voltage, means connecting the resistance elements of saidslope sensing means potentiometer and said slope adjustmentpotentiometer in parallel to said second source of voltage, second motorcontrol means having an output and having an input which is connected tothe wipers of said slope sensing means potentiometer and said slopeadjustment potentiometer; and manually operable switch means selectivelyoperable to connect the outputs of said first and second motor controlmeans each to one or the other of said pair of electric motors.

2. In combination, a paving machine having a propulsion unit and afloated screed, a pair of beams pivotally attached at their forward endto said propulsion unit and rigidly attached at the rear ends to saidscreed, said pav- '11. 1 ing machine being constructed and arranged todeposit paving material beneath said screed such that the angle ofattack of the two ends of the screed in relation to the paved surfacevaries the height of the surface as the paving machine moves to depositthe paving material under the screed, height datum means disposed alongthe route to be paved, a pair of reversible DC. motors, meansoperatively connecting one of said pair of motors to each of said beamsto thereby independently move the same and to independently change theangle of attack of the two ends of said screed upon energization of saidmotors, height sensing means mounted on one of said beams and movabletherewith, said height sensing means cooperating with said height datummeans and including a potentiometer having a resistance element and awiper whose position is controlled by the relative spacing of saidheight sensing means and said height datum means, a vernier adjustmentpotentiometer having a resistance element and a manually movable wiper,a first source of A.C.

voltage, means connecting the resistance elements of said height sensingmeans potentiometer and said vernier adjustment potentiometer inparallel to said first source ct A.C. voltage, first phase sensitivemotor control means having .a reversible polarity DC. output and aninput which is connected to the wipers of said height sensing meanspotentiometer and said vernier potentiometer, slope sensing meanscooperatively associated with each of said beams and having apotentiometer with a resistance element .and a wiper controlled by apendusum, the position of said wiper being indicative of the slope ofsaid screed and the angle of attack of the two ends thereof,

a slope adjustment potentiometer having a resistance element and amanually movable wiper, a second source of A.C. voltage, meansconnecting the resistance elements of said slope sensing meanspotentiometer and said slope adjustment potentiometer in parallel tosaid second source of A.C. voltage, second phase sensitive motor controlmeans having a reversible polarity DC. output and an input which isconnected to the wipers of said slope sensing means potentiometer andsaid slope adjustment potentiometer, manually operable switch meansselectively operable to connect the outputs of said first and secondmotor control means to one or the other of said pair of electric motors,first and second indicating means including first and second electricalmeters disposed to indicate grade error and slope error respectively,and

means connecting said first and second indicating means in parallel withthe input of said first and second motor control means.

3. Control apparatus for use with a paving machine of the floating,screed type wherein it is desired to produce a paved surface of a heightas controlled by height datum means positioned adjacent the surface tobe paved, wherein the paving machine is constructed and arranged with apropulsion unit connected to the floating screed by a pair of beamswhich are rigidly attached to the screed and loosely pivotally attachedto the propulsion unit, the apparatus comprising: motive meansoperatively connected to the beams to change the angle of attack of thescreed, height sensing means mounted on one of the beams and movabletherewith, said height sensing means including a potentiometer having aresistance element and a movable wiper whose position is controlled inaccordance with the relative spacing of said height sensing means andthe height datum means, a vernier adjustment potentiometer having aresistance element and a manually movable wiper, a source of voltage,circuit means connecting the resistance elements of said height sensingmeans potentiometer and said vernier adjustment potentiometer inparallel to said source of voltage, indicating meter means having aninput connected to the wipers of said height sensing means potentiometerand said vernier adjustment potentiometer, further resistance meanshaving a tap and end terminals, means connecting said end terminals tosaid source of voltage, control means having an output connected to saidmotive means, manually operable switch means having an automaticposition and a manual position, circuit means including said last-namedswitch means in the automatic position connecting the input of saidcontrol means to the potentiometer wipers of said height sensing meanspotentiometer and said vernier adjustment potentiometer, and furthercircuit means including said switch means in said manual positionconnecting the input of said control means to the tap of said furtherresistance means and selectively to one or the other of the endterminals of said further resistance means.

4. In combination, a paving machine having a propulsion unit, a floatingscreed, and a pair of beams having one end rigidly connected to saidfloating screed and the other end pivotally connected to said propulsionunit, said propulsion unit being adapted to tow said floating screedsuch that paving material may be deposited in front of said screed andsaid screed rides on the paving material to form a paved surface, theheight of the paved surface being determined by the angle of attack ofsaid screed; height datum means disposed along the surface to be paved,height sensing means mounted on one of said beams and movable therewith,said height sensing means including a member cooperating with saidheight datum means, a height sensing means potentiometer having aresistance element and a movable wiper whose position is controlled bythe member of said height sensing means, a vernier adjustmentpotentiometer having a resistance element and a manually movable wiper,a source of A.C. voltage, circuit means connecting the resistanceelements of said height sensing means potentiometer and said vernieradjustment potentiometer in parallel to said source of voltage; motivemeans operatively connected to said one of said beams to control theangle of attack of one end of said screed, said motive means having aninput including a first and a second terminal, circuit means connectingsaid first terminal to a reference potential; first manually operableswitch means having an automatic and a manual position, circuit meansincluding said first manual switch means in said automatic positionconnecting the potentiometer wiper of said height sensing meanspotentiometer to said reference potential and connecting the other inputterminal of said motive means to the potentiometer wiper of said vernieradjustment potentiometer; a resistance element having a pair of endterminals and a tap, circuit means connecting said end terminals to saidsource of voltage; second manually operable switch means having anormally open position and a first and second closed position, circuitmeans including said first switch means in said manual positionconnecting the tap of said resistance element to said referencepotential, and further circuit means including said first switch meansin said manual position connecting the other input terminal of saidmotive means selectively through said second switch means to one of theend terminals of said resistance element.

5. In combination, a paving machine of the floated screed type having apropulsion unit and a floated screed which is towed behind thepropulsion unit by means of a pair of beams which are pivoted at theirforward end to the propulsion unit and which are rigidly attached to thefloated screed, the paving machine including means adapted to depositpaving material under the floated screed, first and second reversibleDC. motors, means connecting said motors one to each of said beams tovary the position of its beam and change the angle of attack of the endsof said screed; datum means establishing a height reference along theroute to be paved, height sensing means disposed on one of said beamsand movable therewith, said heightvsensing means including meanscooperating with said height datum means and including a potentiometerhaving a wiper whose position is controlled by said height sensing meansto provide an indication of the relative position of said height sensingmeans and said height datum means; a pendulum supported by said beamsand including a potentiometer whose resistance element is moved by saidpendulum such that the position of said wiper is indicative of the slopeof said screen and the angle of attack of the ends of said screed; afirst A.C. bridge circuit including a first source of A.C. voltage, saidheight sensing means potentiometer, and an adjustment potentiometerhaving a manually movable wiper; first indicating meter means having aninput connected to the wipers of said height sensing means potentiometerand said adjustment potentiometer; a first impedance element having atap and end terminals connected to said first source of voltage; a firstphase sensitive motor control circuit providing a reversible polarityDC. output and having a pair of input terminals, one of which isconnected to a reference potential; first manually operable switch meanshaving an automatic and a manual position, said first switch means insaid automatic position connecting the wiper of said height sensingmeans potentiometer to said reference potential and connecting thesecond input terminal of said first motor control circuit to the wiperof said adjustment potentiometer; second manually operable switch meanshaving a normally open condition and a first and a second closedcondition, said first switch means in said manual position connectingthe tap of said first impedance element to said reference potential andconnecting the second input terminal of said first motor control circuitto said second switch means, circuit means including said second switchmeans connecting said second input terminal of said first motor controlcircuit selectively to one of said end terminals of said first impedanceelement; a second A.C. bridge circuit including a second source of A.C.voltage, said pendulum potentiometer, and a slope adjustmentpotentiometer having a manually movable wiper; second indicating metermeans having an input connected to the wipers of said pendulumpotentiometer and said slope adjustment potentiometer; a secondimpedance element having a tap and end terminals connected to saidsecond source of voltage; a second phase sensitive motor control circuitproviding a reversible polarity DC. output and having a pair of inputterminals, one of which is connected to said reference potential; thirdmanually operable switch means having an automatic and a manualposition; said third switch means in said automatic position connectingthe wiper of said pendulum potentiometer to said reference potential andconnecting the second input terminal of said second motor controlcircuit to the wiper of said slope adjustment potentiometer; fourthmanually operable switch means having a normally open condition and afirst and a second closed condition, said third switch means in saidmanual position connecting the tap of said second impedance element tosaid reference potential and connecting the second input terminal ofsaid second motor control means to said fourth switch means, circuitmeans including said fourth switch means connecting said second inputterminal of said second motor control circuit selectively to one of thesaid terminals of said second impedance element; and further manuallyoperable switch means selectively operable to connect the outputs ofsaid first and second motor control means to one or the other of saidfirst or second motors.

6. Control apparatus for use with a floating screed paving machine, inwhich the screed is towed behind a propulsion unit and the height andslope profile of a resulting road surface is controlled by independentlycontrolling the angle of attack of the opposite ends of the screed, theapparatus comprising; height sensing means vertically movably mounted inrelation to the paving machine and carried thereby, control means havingan input connected to be controlled by said height sensing means andhaving an output connected to control the angle of attack of one end ofthe screed and to concurrently move said height sensing means verticallyrelative to the paving machine; slope sensing means mounted in relationto the screed to be responsive to the transverse slope of the screed andto the angle of attack of the opposite ends of the screed, and controlmeans having an input connected to be controlled by said slope sensingmeans and having an output connected to control the angle of attack ofthe other end of the screed.

7. Control apparatus for use with a floating screed paving machine, inwhich a transversely extending screed is towed behind a propulsion unitby means of a pair of beams, one of which is attached to each end of thescreed and is also pivoted to the propulsion unit at the forward end ofthe beams, and the height and slope profile of a resulting road surfaceis controlled by independently controlling the angle of attack of theopposite ends of the screed by vertical movement of the beams, theapparatus comprising; height datum sensing means, means adapted to mountsaid sensing means on one of the beams such that movement of that one ofthe beams causes vertical movement of said sensing means as the angle ofattack of one end of the screed is changed; slope attitude responsivemeans adapted to be mounted on both of the beams to sense the slope ofthe screed and the angle of attack of each end of the screed; andcontrol means having input means connected to be controlled by saidsensing means and by said responsive means, and having output meansadapted to affect independent vertical movement of said one of the beamsby said sensing means and the other of the beams by said responsivemeans,

8. Control apparatus for use with a paving machine of the floatingscreed type to automatically control the angle of attack of one end ofthe screed thereof in accordance with a predetermined height referencedatum and thus control the surface of the road being produced as thepaving machine moves, comprising: height datum sensing means mountedwith reference to said one end of the screed and having movable controlmeans adapted to cooperate with the height reference datum, said sensingmeans being vertically movable as the angle of attack of said one end ofthe screed is varied and having an electrical transducer whose controlelement is moved by movement of said control means; a control electricaltransducer having a manually movable control element, a source ofvoltage, means connecting said sensing means transducer and said controltransducer to said source of voltage; motive means connected to thescreed to control the angle of attack of said one end thereof uponactuation of said motive means, to thereby produce a subsequent changein vertical position of said sensing means relative to the referencedatum as the screed angle of attack changes; and electrical controlmeans for said motive means, said electrical control means having aninput connected to said sensing means transducer and said controltransducer and having an output connected to said motive means.

9. In combination, a paving machine of the floated screed type having apropulsion unit including motive means to move the paving machine, afloating screed, said screed being attached to said propulsion unit by apair of spaced beams which are pivoted to the propulsion unit at theforward end of the beams and are rigidly attached to the screed at therear end of the beams so that vertical movement of the beams changes theangle of attack of spaced portions of the screed, grade reference meansestablishing a grade reference for the paved surface, grade sensingmeans mounted on one of said beams to be vertically movable therewithand cooperating with said grade reference means, said sensing meansincluding a potentiometer whose wiper is moved in accordance withdeviations in relative position of said sensing means and said gradereference means, a further potentiometer having a manually movablewiper, a source of voltage, circuit means connecting the resistanceelements of said sensing means potentiometer and said furtherpotentiometer to said source of voltage, motive means connected incooperating relation to said one of said beams to move said one beam andthereby vary the angle of attack of one portion of the screed, controlmeans having an output connected to said motive means and having aninput connected to the wipers of said sensing means potentiometer andsaid further potentiometer to apply an error signal thereto upon avariation in the relative position of said sensing means and said gradereference means, indicating means, and means connecting said indicatingmeans to the Wipers of said sensing means potentiometer and said furtherpotentiometer to apply an input thereto to thus provide an indication ofsuch variation.

10. Control apparatus for use with a paving machine of the floatingscreed type wherein the screed is towed behind a propulsion unit, thefloating screed resting on the resulting paved surface by virtue of theweight of the screed and the thickness and slope of the paved surfacebeing determined by the angle of attack of the two ends of the screed,the control apparatus comprising: a pair of motive means, a first ofwhich is associated with one end of the screed and a second of which isassociated with the other end of the screed, to independently controlthe angle of attack of the ends of the screed; grade sensing meansmounted ahead of said one end of the screed and adapted to cooperatewith grade datum means which forms a predetermined grade; slope sensingmeans associated with each end of the screed and responsive to the slopeof the screed and to the angle of attack of the ends of the screed; afirst potentiometer having a resistance element and a wiper whoseposition is controlled by said grade sensing means; a secondpotentiometer having a resistance element and a wiper whose position iscontrolled by said slope sensing means; a Vernier adjustmentpotentiometer having a manually movable wiper, a first bridge networkincluding a source of voltage connected to said first potentiometer andto said vernier adjustment potentiometer; a slope adjustmentpotentiometer having a manually movable wiper, a second bridge circuitincluding a source of voltage connected to said second potentiometer andto said slope adjustment potentiometer; first and second control meanseach having an input and an output, means connecting the output of saidfirst control means to said first motive means, means connecting theoutput of said second control means to said second motive means; meansconnecting the input of said first control means to the potentiometerwipers of said first bridge circuit to thus automatically control theangle of attack of said one end of the screed in accordance with thegrade sensing means; and means connecting the input of said secondcontrol means to the potentiometer wipers of said second bridge circuitto thus automatically control the angle of attack of the other end ofthe screed in accordance with the slope sensing means.

11. Control apparatus for use in automatically controlling the angle ofattack of the screed of a floated screed paving machine, to maintain apredetermined grade and slope road profile, the floated screed beingtowed by means of first and second spaced beams which are rigidlyattached to first and second ends respectively of the floated screed atthe rear end of the beams, said paving machine being adapted tocooperate with grade datum means establishing the grade for a resultantpaved surface, the control apparatus comprising: first and second motivemeans each of which is cooperatively associated with the first andsecond beams respectively to control the position of its beam and thusvary the angle of attack of said first and'second ends of the fioatedscreed; grade sensing means movably positioned forward said first end ofthe screed and having a potentiometer whose wiper is adjusted by meanscooperating with the grade datum means, the relative position of saidgrade sensing means and the grade datum means varying by virtue ofunevenness of the surface to be paved by the paving machine and byvirtue of movement of said one beam by operation of its associatedmotive means; a pendulum supported on said beams and responsive to theslope of the scIeed and 1 .0 the angle of attack of said first id andsecond ends of the screed, a second potentiometer having a wiper whoseposition is determined by said pendulum; a Vernier adjustmentpotentiometer having a manually movable wiper, a first bridge circuitincluding a tion of said grade sensing means; a slope adjustmentpotentiometer having a manually movable wiper which is manually moved toproduce the desired slope to the resulting paved surface, and secondcontrol means having an input connected to the potentiometer wipers ofsaid pendulum potentiometer and said slope adjustment potentiometer andhaving an output connected to said second motive means.

12. Control apparatus for use in automatically controlling the angle ofattack of one end of the screed of a floating screed road paving machineto maintain a predetermined grade profile as established by a gradedatum, the control apparatus comprising: grade datum sensing meansadapted to be mounted to move vertically as the angle of attack of theone end of the screed is varied, and

p as irregularities in the surface to be paved are encountered, a firstpotentiometer whose wiper moves as said sensing means is movedvertically; a Vernier adjustment potentiometer having a manually movablewiper; a source of voltage, means connecting said first potentiometerand said adjustment potentiometer to said source of voltage to form abridge network; voltage responsive motive means adapted to be placed incontrolling relation to control the angle of attack of the one end ofthe screed; a switch having a manual and an automatic position, meanscontrolled by said switch in said automatic position connecting saidmotive means to the wipers of said first potentiometer and saidadjustment potentiometer to be controlled by the bridge voltage at saidwipers to achieve automatic control of the angle of attack of the oneend of the screed, and means controlled by said switch in said manualposition adapted to selectively connect said motive means to a source ofvoltage to achieve manual control of the angle of attack of the one endof the screed.

13. Control apparatus for use in automatically controlling the angle ofattack of one end of the screed of a floating screed road paving machineto maintain a predetermined slope profile, the control apparatuscomprising: slope sensing means adapted to be mounted to sense the slopeand the angle of attack of the one end of the screed, which factors varyas the angle of attack of the one end of the screed is varied and asirregularities in the surface to be paved are encountered, a firstpotentiometer whose wiper moves as said sensing means senses a change insaid factors; a slope adjustment potentiometer having a manually movablewiper; a source of voltage, means connecting said first potentiometerand said adjustment potentiometer to said source of voltage to form abridge network; voltage responsive motive means adapted to control theangle of attack of the one end of the screed; a switch having a manualand an automatic position, means controlled by said switch in saidautomatic position connecting said motive means to the wipers of saidfirst potentiometer and said adjustment potentiometer to be controlledby the bridge voltage at said wipers to achieve automatic control of theangle of attack of the one end of the screed, and means controlled bysaid switch in said manual position adapted to selectively connect saidmotive means to a source of voltage to achieve manual control of theangle of attack of the one end of the screed.

14. Control apparatus for use to stabilize a movable elongated memberboth as to slope and height, the apparatus comprising: a slope sensoradapted to be connected to the member to sense the transverse slopethereof, control means having an input connected to be controlled bysaid slope sensor, motive means connected to be controlled by the outputof said control means and adapted to move one end of the member tomaintain a desired slope; a height sensor adapted to be connected to themember at a position spaced from said one end to sense the height ofsaid position, second control means having an input connected to becontrolled by said height sensor and second motive means connected to becontrolled by the output of said second control means and adapted2,295,519 9/ 42 Millikin 9446 2,491,275 12/49 Millikin 9446 2,922,345 1/60 Mentes 9446 3,029,715 4/ 62 Bowen 9446 3,029,716 4/62 Shea 94463,111,070 11/63 Pollitz 9446 JACOB L. NACKENOFF, Primary Examiner.

6. CONTROL APPARATUS FOR USE WITH A FLOATING SCREED PAVING MACHINE, INWHICH THE SCREED IS TOWED BEHIND A PROPULSION UNIT AND THE HEIGHT ANDSLOPE PROFILE OF A RESULTING ROAD SURFACE IS CONTROLLED BY INDEPENDENTLYCONTROLLING THE ANGLE OF ATTACK OF THE OPPOSITE ENDS OF THE SCREED, THEAPPARATUS COMPRISING; HEIGHT SENSING MEANS VERTICALLY MOVABLY MOUNTED INRELATION TO THE PAVING MACHINE AND CARRIED THEREBY, CONTROL MEANS HAVINGAN INPUT CONNECTED TO BE CONTROLLED BY SAID HEIGHT SENSING MEANS ANDHAVING AN OUTPUT CONNECTED TO CONTROL THE ANGLE AT ATTACK OF ONE END OFTHE SCREED AND TO CONCURRENTLY MOVE SAID HEIGHT SENSING MEANS VERTICALLYRELATIVE TO THE PAVING MACHINE; SLOPE SENSING MEANS MOUNTED IN RELATIONTO THE SCREED TO BE RESPONSIVE TO THE TRANSVERSE SLOPE OF THE SCREED ANDTO THE ANGLE OF ATTACK OF THE OPPOSITE ENDS OF THE SCREED, AND CONTROLMEANS HAVING AN INPUT CONNECTED TO BE CONTROLLED BY SAID SLOPE SENSINGMEANS AND HAVING AN OUTPUT CONNECTED TO CONTROL THE ANGLE OF ATTACK OFTHE OTHER END OF THE SCREED.